The present invention relates to screw rods, and particularly to a pressure releasing material feeding screw rod used in a melting metal material injection machine.
FIG. 1 shows a prior art injection machine used with a mold. In use, the material is melt as melting material S which is then pushed by a material feeding device 1 to the mold through an injecting nozzle 11. Conventionally, the material is plastic material since the plastic material has lower melting point, fine particles and uniform particle sizes. Thereby, the material feeding screw rod 12 with a simple structure can be used.
However, recently, other materials, especially metals, such as magnesium, aluminum, etc., are used in many products, for example, computer casing. The melting point, cooling speeds, and other physical properties are different from the prior plastic material so that the operation and machine used must be modified.
The density and mass of metal are higher than plastics, but the uniformity thereof is worse than plastics. Referring to FIG. 1, a screw rod has threads 121 will push melting material forwards each two threads has a uniform gap A1, height A2 and width A3). Thereby, the pressure from the melting material applied to the thread can not be released. In one modified structure, the screw rod is divided into three sections, the threads in different sections have different distances, heights and widths, but in this modified prior art, the melting metal material is possibly left in gaps between two threads of the same section. Thereby, the pressure can not be released.
If the screw rod 12 moves forwards continuously, the melting metal material will accumulate between two threads and then apply a force to the surfaces of the threads. Thereby, the cylinder 13 will accumulate too much material therein. Through a long time period, the screw rod 12, threads 121 and cylinder 13 will be destroyed. In some developed designs, the strength of the screw rod 12 and threads 121 are enhanced, but this will further increase the possibility of the accumulation of material in the cylinder.
Accordingly, the primary object of the present invention is to provide a pressure releasing material feeding screw rod used in a material feeding cylinder of a material feeding device of the melting metal material injection machine. A plurality of adjacent threads are arranged along a longitudinal direction of the screw rod. The threads include a plurality of normal pressure threads and a plurality of pressure reduction threads. Each of the normal pressure threads is positioned in front of a respective pressure reduction thread; the normal pressure thread can push the melting material toward the injecting nozzle. An edge of each pressure reduction threads have a gap with a wall of the material feeding cylinder. By the arrangement of the pressure reduction thread, when the normal pressure threads push the melting material forwards, as the melting material in the material feeding cylinder generates an overlarge reacting force on a surface of the normal pressure thread, the gap will receive the material. Then the material will be pushed by next normal pressure thread.
Another object of the present invention is to provide a pressure releasing material feeding screw rod. A plurality of adjacent threads are arranged along a longitudinal direction of the screw rod; the threads include a plurality of normal pressure threads and a plurality of pressure reduction threads. Each of the normal pressure threads is positioned in front of a respective pressure reduction thread. The normal pressure thread can push the melting material toward the injecting nozzle; the pressure reduction threads are flexible. By the arrangement of the pressure reduction thread, when the normal pressure threads push the melting material forwards, as the melting material in the material feeding cylinder generates an overlarge reacting force on a surface of the normal pressure thread, the pressure reduction thread will be pushed to bent backwards so as to form a gap between the pressure reduction threads and a wall of the material feeding cylinder. Then the material will pass through the gap; and then the material is pushed by next normal pressure thread.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing.